Humidistat



April 15, ,1969 R. M. ANDERSON HUMIDISTAT Filed Oct. 2G. 1966 a ETW/7 United States Patent 3,439,136 HUMIDISTAT Robert M. Anderson, 1071 E. 54th St., Indianapolis, Ind. 46220 Filed Oct. 26, 1966, Ser. No. 589,726 Int. Cl. H01h -35/42 U.S. Cl. 200--61.06 7 Claims ABSTRACT OF THE DISCLOSURE An electromechanical humidistat in which a hygroscopic element is coupled to a selector and a tensioning bar. Elongation of the hygroscopic element permits the bar to move to operate a pair of switches. An adjustable dead band is provided by staggering the operating points of the two switches.

This invention relates generally to humidity control devices, commonly referred to as humidistats.

Many applications of humidity control exist today, such as in computer rooms, laboratories, greenhouses and microwave radio equipment rooms. Humidity control is required Wherever equipment performance or desirable results, such as in plant growth, may be adversely affected by humidity or fluctuations in humidity.

Expensive electronic devices for humidity control having a dead band and high accuracy are known in the art, but these devices are in many applications uneconomical because of their high cost, or undesirable because they are not rugged enough to function properly in the environment where humidity control is desired. Inexpensive lhumidistats of fairly simple construction are also known in the art, but these devices either provide ruggedness at the expense of accuracy, or provide relatively good accuracy at the expense of ruggedness, such as in the devices that employ a human hair as the hygroscopic element.

It is therefore an object of this invention to provide an improved humidistat of simplified and rugged construction.

It is a further object of this invention to provide such a humidistat that is relatively inexpensive to manufacture and is economical to use in a wide variety of applications.

It is a still further object of this invention to provide a humidistat having a dead band.

Still another object of the invention is to provide a humidistat which is completely mechanical in nature so that it can be serviced by persons unskilled in electronics.

Related objects and advantages will become apparent as the description proceeds.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

FIG. 1 is a plan view of the humidistat of this invention showing the chassis and internal elements with the cover removed.

FIG. 2 is a sectional view of the humidistat of this invention taken along the line 2-2 of FIG. l.

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawing and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates,

ICC

Referring now more particularly to the drawings, there is illustrated a chassis 11 having a base portion 12, a rear portion 13, a front portion 14, angle portions 16 providing support for the said front portion and a depression 17. In the preferred embodiment of the invention, said base portion, rear portion, front portion and angle portions of the chassis are integral, being unitarily cast of aluminum or other suitable metal.

Mounted on the front portion 14 of the chassis is a selector means, indicated generally at 21 and including a threaded rotatable shaft 22 extending through a hole 23 in the front portion 14 of the chassis and axially restrained from moving inwardly of the chassis by the shoulder 22a of the shaft 22 as best shown in FIG. 2. A cylinder 26 is threadedly coupled to the threaded shaft 22 and is restrained from rotating about the axis of the threaded shaft 22 by a restraining element 27 affixed to the front portion 14 of the chassis by a metal screw 28 and lock washer 28a. A selector knob 29 attached to the threaded shaft 22 by a set screw 29a facilitates manual rotation of the threaded shaft 22, In the preferred ernbodiment, the selector knob 29 includes a pointer 29b, and said pointer cooperates with the metal screw 28 as a stop device limiting rotation of the threaded shaft 22 to slightly less than one full revolution. The threaded shaft 22, cylinder 26 and restraining element 27 are arranged, as best shown in FIG. 2, to translate the cylinder 26 in a direction parallel to the axis of the threaded shaft 22 when the threaded shaft 22 is rotated.

Tensioning means, indicated generally at 31 includes a bar 32, spring element 33 and a clamp plate 34 fastened to the chassis within the depression 17 by a machine screw 36, as best shown in FIG. 2. The spring element has a generally U-shaped portion 33a which underlies the clamp plate 34. Extending upwardly from the ends of the U- shaped portion 33a are vertical portions 33b. At the upper extremity of each vertical portion 33-b is a short horizontal portion 33C which connects the spring element to the bar 32. In the preferred embodiment the spring element is bendingly formed from a single piece of spring steel wire stock. The clamp plate 34 is L-shaped in cross section and clamps the 'U-shaped portion 33a of the spring element 33 rigidly to the chassis as best shown in FIG. 2. The tensioning means operates to exert a force in line with the axis of the threaded shaft 22 of the selector means 21 and directed toward the rear portion 13 of the chassis.

Operatively coupled to the selector means and to the tensioning means is a hygroscopic element 4'1. In the preferred embodiment of the invention, the hygroscopic element 41 comprises a sheet of treated cellulose material wrapped around the cylinder 26 of the selector means and the bar 32 of the tensioning means. The cellulose material is stitched together at its ends by stitching 42 to form a belt and has a cut-out portion 43 to accommodate the entrance of the threaded shaft 22 into the cylinder 26.

Switch means, indicated generally at 51 comprises two mechanically operated electrical switches 52. The switches 52a and 52h are operably positioned with respect to the bar 32 of the tensioning means and operated thereby. The switches 52 are of a configuration wherein only a very small mechanical motion is required to operate the electrical contacts thereof. In the preferred embodiment, each switch 52 has a normally open contact (not shown) and a normally closed contact (not shown) and has an operating nipple 53 and a spring guard 54 as best shown in FIG. 1.

An adjusting means, indicated generally at 61, is attached to the chassis as best shown in FIG. 2. The adjusting means includes a movable upper plate 62 and a stationary lo'wer plate 63 pivotally connected together at 64.

The lower plate 63 is fastened to the chassis and the upper plate is fastened to a switch 52, preferably by machine screws. A V-shaped opening 66 in the lower plate and saw-toothed members 67 on the upper plate permit accurate positioning of the upper plate with respect to the lower plate by means of a screwdriver and thereby positioning the switch 52 with respect to the cylinder 32 of the tensioning means. The machine screw 68 and lock washer 68a provide means for securely fastening the said plates in the desired relative position.

In operation, the hygroscopic element is tensioned between the selector means and the tensioning means. The hygroscopic element is responsive to changes in the relative humidity of its environment, elongating with an increase in and contracting with a decrease in the relative humidity. In the preferred embodiment of the invention, the treated cellulose material exhibits a substantially linear characteristic between twenty and ninety percent relative humidity.

As the relative humidity increases, the hygroscopic element elongates, permitting the bar 32 of the tensioning means to move toward and operate the switches 52 closing the normally open and opening the normally closed contacts. As the relative humidity decreases, the hygroscopic element contracts, moving the bar 32 of the tensioning means away from the switches 52 allowing said contacts to return to their normal positions.

The use of two switches 52 and the adjusting means 6,1 provides an adjustable dead band in the operating characteristic of the humidistat. This permits a humidifier and a dehumidifier to be controlled by the humidistat in a manner that prevents hunting and fighting between the humidifier and dehumidifier. If just one switch were used, a humidifier being connected to the normally closed contact and a dehumidifier connected to the normally open contact, one or the other would be running continuously, first driving the relative humidity of the environment upward and then downward, resulting in considerable inefficiency and excessive power consumption. With a dead band in the control characteristic of the humidistat, neither the humidifier nor the dehumidifier runs when the relative humidity is within the acceptable range.

The dead band is provided by staggering the operating points of the switches 52. One of the switches, such as 52b, is positioned by the adjusting means `61 a small distance rearwardly of the switch 52a. Thus, as the relative humidity increases, the hygroscopic element elongates, and the bar 32 of the tensioning means moves rearwardly, switch 52a is rst operated. A humidifier connected to the normally closed contact of switch 52a is then turned off as the normally closed contact opens. If the relative humidity continues to increase, further elongation of the hygroscopic element occurs, allowing the bar 32 to move still further rearwardly and operate switch 52h. A dehumidifier connected to the normally open contact of switch 52b then begins to run when the normally open contact closes. When the bar 32 is between the operating points of switch 452a and switch 52b, it is within the dead band where neither the humidifier nor the dehumidifier is running.

Because humidity cannot be changed instantaneously, there is inherent time lag in any humidity control system. 'Ilhis inherent time lag can cause undesirable overshoot. That is, if the humidifier is running, by the time the air surrounding the humidistat has reached the desired relative humidity, a portion of the remainder of the air in the room is too Iwet and as the moisture diffuses throughout the room the relative humidity as sensed by the humidistat continues to rise after it has turned off the humidifier. The humidistat thereupon turns on the dehumidifier, and the same process would occur in reverse. That is, by the time the humidistat sensed dry enough air to turn off the dehumidifier, enough of the air in the room would be too dry, and as the moisture diffused through the room, the relative humidity of the air surrounding the humidistat would continue to fall, causing the humidistat to turn on the humidifier. Thus, the cycle would repeat itself. With an adjustable dead band characteristic as provided by the humidistat of the present invention and proper sizing and `design of the humidifier and dehumidifier, continuous cycling can be eliminated by proper selection of the dead band for each specific application.

The humidistat of the present invention may also be used to control two humidiliers or two dehumidifiers. In an application Where only dehumidifying is required, for example, one dehumidifier may be connected to the normally open contact of each switch 52. When the relative humidity is below the desired maximum, neither humidifier runs. As the humidity rises, one of the switches, suoh as 52a, operates, closing its normally open contact and thereby starting the first dehumidifier. If, with the first dehumidifier running, the humidity continues to increase, the other switch 52b will operate and turn on the second dehumidifier. In this manner, only the necessary 'dehumidfying capacity is operated. It will be apparent to those skilled in the art that such an arrangement minimizes overshoot and provides closer control and allows more flexibility in the overall design of the humidity conditioning system.

It will be evident from the above detailed description that this invention provides an improved humidistat of simple and rugged construction that is relatively inexpensive to manufacture and is economical to use in a wide variety of applications. It will also be evident that the humidistat of this invention provides a dead band, yet is substantially mechanical in nature so that it can be serviced by persons unskilled in electronics.

While the invention Ihas been illustrated /and described in detail in the drawing and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and `described and that all changes and modifications that come Within the spirit of the invention and the scope of the claims are also desired to be protected.

The invention claimed is:

1. In a humidistat, the combination comprising:

(a) a hygroscopic element adapted to respond to the relative humidity of its environment;

(b) first electrical switch means being cooperatble with said hygroscopic element to actuate first electrical contacts;

(c) first adjusting means coupled to said first electrical switch means and being cooperable therewith and i with said hygroscopic element to adjust the relative humidity at which said first electrical contacts are actuated;

(d) second electrical switch means being cooperable with said hygroscopic element to actuate second electrical contacts;

(e) second adjusting means coupled to said second electrical switch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said second electrical contacts are actuated; and

(f) selector means coupled to said hygroscopic element and cooperable therewith and with both said first adjusting means and said second adjusting means for selecting the relative humidity at which said first electrical contacts and said second electrical contacts are actuated, said hygroscopic element being a belt of treated cellulose material having an opening therein and the selector means including a cylinder and a rotatable shaft passing through said opening in said treated cellulose material and being threadedly coupled to said cylinder, the belt of treated cellulose material partially overlying said cylinder.

2. In a humidistat, the combination comprising:

(a) a hygroscopic element adapted to respond to the relative humidity -of its environment;

(b) first electricalA switch means being cooperable with said hygroscopic element to actuate first electrical contacts;

(c) first adjusting means coupled to said rst electrical switch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said first electrical contacts are actuated;

(d) second electrical switch means being cooperable with said hygroscopic element to actuate second electrical contacts;

(e) second adjusting means coupled to said second electrical switch means and 'being cooperable therewith said with said hygroscopic element to adjust the relative humidity at which said second electrical contacts are actuated; ancl- (f) tensioning means for maintaining said hygroscopic element under mechanical tension and being cooperable therewith and with said first electrical switch means and with said second electrical switch means to actuate said electrical contacts and said second electrical contacts, said hygroscopic element being a belt of treated cellulose material and the tensioning means including a bar and a spring element connected thereto, the belt of treated cellulose material partially overlying and being tensionedby said bar.

3. In a humidistat, the combination comprising:

(a) a hygroscopic element adapted to respond to the relative humidity of its environment;

(b) first electrical switch means being cooperable with said hygroscopic element to actuate first electrical contacts;l

(c) first adjusting means coupled to said first electrical switch means and being cooperable therewith and with said hygros-copic element to adjust the relative humidity at which said first electrical contacts are actuated;

(d) second electrical switch means being cooperable with said hygroscopic element to actuate second electrical contacts;

(e) second adjusting means coupled to said second electrical switch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said second electrical contacts are actuated; and

(f) tensioning means for maintaining said hygroscopic element under mechanical tension and being cooperable therewith and with said first electrical switch means and with said second electrical switch means to actuate said -first electrical contacts and said second electrical contacts, said tensioning means including a bar, the electrical switch means being in the path of and mechanically operated -by said bar of the tensioning means.

4. In a humidista't, the combination comprising:

(a) a hygroscopic element adapted to respond to the relative humidity of its environment;

(b) first electrical switch means being cooperable with said hygroscopic element to actuate first electrical contacts;

(c) first adjusting means coupled to said first electrical switch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said first electrical contacts are actuated;

(d) second electricalV switch means being cooperable with said hygroscopic element to actuate solenoid electrical contacts;

(e) second adjusting means coupled to said second electrical switch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said second electrical contacts are actuated; and

(f) tensioning means for maintaining said hygroscopic element under mechanical tension and being cooperable therewith and with said first electrical switch means and with said second electrical switch means to actuate said first electrical contacts and said second electrical contacts, the adjusting means including a stationary lower plate, a movable upper plate supporting a switch means and pivotally connected to said lower plate, and means for securely fastening said plates in the desired relative position.

5. In a humidistat, the combination comprising:

(a) a hygroscopic element adapted to respond to the relative humidity of its environment;

(b) first electrical switch means being cooperable with said hygroscopic element to actuate first electrical contacts;

(c) first adjusting means coupled to said first electrical switch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said first electrical contacts are actuated;

(d) second electrical switch means being cooperable with said hygroscopic element to actuate second electrical contacts;

(e) second adjusting means coupled to said second electrical swit-ch means and being cooperable therewith and with said hygroscopic element to adjust the relative humidity at which said second electrical contacts are actuated; and

(f) tensioning means for maintaining said hygroscopic element under mechanical tension and being cooperable therewith and with said first electrical switch means and with said second electrical switch means to actuate said first electrical contacts and said second electrical contacts, selector means coupled to said hygroscopic element and cooperable therewith and with both said first adjusting means and said second adjusting means for selecting the relative humidity at which said first electrical contacts and said `second electrical contacts are actuated.

6. The combination of claim 5 wherein said hygroscopic element is a belt of treated cellulose material having an opening therein and the selector means includes a cylinder and a rotatable shaft passing through said opening in said treated cellulose material and being threadedly coupled to said cylinder, and the tensioning means includes a bar and a spring element connected thereto, the belt of treated cellulose material partially overlying said bar and said cylinder, and being mechanically tensioned between said -cyinder and said bar.

7. In a humidistat the combination comprising a base, a first electrical switch mounted on said base, a second electrical switch mounted on said base, a belt of material adapted to change in dimension in accordance with a change in relative humidity, a pair of rods received 'within said belt, means for securing one of said rods to said base, spring means acting between the other rod and said base and urging the other rod toward said electrical switches for the actuation thereof, said other rod being retained by said belt which is held taut by said rods, said switches being individually adjustable as to position on said base for adjusting the relative humidity at which said switches are actuated, said means for securing one of said rods to said base incorporating selector means operable to adjust the position of said one rod relative to said base for selecting the relative humidity at which said switches are actuated.

References Cited UNITED STATES PATENTS 1,833,383l 1/1931 Stacey 20G-61.06 1,968,301 3/1930 Lewis 20D-61.06 2,198,131 4/1940 Shaw 200--61.06 3,163,729 12/1964 Flagg ZOO-61.06

BERNARD A. GILHEANY, Primary Examiner.

FRED E. BELL, Assistant Examiner. 

